Rh-Catalyzed [3 + 2] Cycloaddition of 1‑Sulfonyl-1,2,3-triazoles: Access to the Framework of Aspidosperma and Kopsia Indole Alkaloids

A Rh­(II)-catalyzed
dearomative intramolecular [3 + 2] dipolar cycloaddition
involving the indolic C2–C3 carbon–carbon double bond
has been developed. The reaction was launched from the triazole moiety
within the substrate and proceeded efficiently under mild conditions.
A wide range of functional groups could be tolerated. These features
render the current reaction a highly useful tool for the synthesis
of polycyclic indole alkaloids, as showcased by a rapid assembly of
the core structure of Aspidosperma and the related alkaloids.